2.2.7 Arcs

Arc objects are specified by center position, radius, and start
and end angles. They are purely graphical with no electrical
meaning. They can be drawn in different colors, and with various
stroke settings.

— Function: arc? object

Returns ‘#t’ if and only if object is an arc object.

— Function: make-arc center radius start-angle end-angle [color]

Creates and returns a new arc object. center is the
position of the center of the new arc in the form (x . y), and
radius is the integer radius of the arc. start-angle and
end-angle are the angles at which to start and end the arc, in
degrees. If color is specified, it should be the integer color
map index of the color with which to draw the arc. If color
is not specified, the default arc color is used.

— Function: set-arc! arc center radius start-angle end-angle [color]

Sets the parameters of arc. The arguments are the same as to
make-arc. Returns arc.